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• Node & Redis: Crucial Design Issues in Production Mode

  - by Ali

  This question is a hybrid one, being both technical and system design related. I'm developing the backend of an application that will handle approx. 4K request per second. We are using Node.js being super fast and in terms of our database struction we are using MongoDB, with Redis being a layer between Node and MongoDB handling volatile operations. I'm quite stressed because we are expecting concurrent requests that we need to handle carefully and we are quite close to launch. However I do not believe I've applied the correct approach on redis. I have a class Student, and they constantly change stages(such as 'active', 'doing homework','in lesson' etc. Thus I created a Redis DB for each state. (1 for being 'active', 2 for being 'doing homework'). Above I have the structure of the 'active' students table; xa5p - JSON stringified object #1 pQrW - JSON stringified object #2 active_student_table - {{studentId:'xa5p'}, {studentId:'pQrW'}} Since there is no 'select all keys method' in Redis, I've been suggested to use a set such that when I run command 'smembers' I receive the keys and later on do 'get' for each id in order to find a specific user (lets say that age older than 15). I've been also suggested that in fact I used never use keys in production mode. My question is, no matter how 'conceptual' it is, what specific things I should avoid doing in Node & Redis in production stage?. Are they any issues related to my design? Students must be objects and I sure can list them in a list but I haven't done yet. Is it that crucial in production stage?

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• HOWTO: implement a jQuery version of ASP.Net MVC "Strongly Typed Partial Views"

  - by Sam Carleton

  I am working on a multi-page assessment form where the questions/responses are database driven. Currently I the basic system working with Html.BeginForm via standard ASP.Net MVC. At this point in time, the key to the whole system is the 'Strongly Typed Partial Views'. When the question/response is read from the database, the response type determines which derived model is created and added to the collection. The main view it iterates through the collection and uses the 'Strongly Typed Partial Views' system of ASP.Net MVC to determine which view to render the correct type of response (radio button, drop down, or text box). I would like to change this process from a Html.BeginForm to Ajax.BeginForm. The problem is I don't have a clue as to how to implement the dynamic creation of the question/response in the JavaScript/jQuery world. Any thoughts and/or suggestions? Here is the current code to generate the dynamic form: @using (Html.BeginForm(new { mdsId = @Model.MdsId, sectionId = @Model.SectionId })) { <div class="SectionTitle"> <span>Section @Model.SectionName - @Model.SectionDescription</span> <span style="float: right">@Html.CheckBoxFor(x => x.ShowUnansweredQuestions) Show only unaswered questions</span> </div> @Html.HiddenFor(x => x.PrevSectionId) @Html.HiddenFor(x => x.NextSectionId) for (var i = 0; i < Model.answers.Count(); i++) { @Html.EditorFor(m => m.answers[i]); } }

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• Bulletin board - Database optimisation

  - by andrew

  This question is a follow on from this Question The project and problem The project I am currently working on is a bulletin board for a large non-profit organisation. The bulletin board will be used to allow inter-office communication within the organisation. I am building the application and have been having trouble extracting the results that I need from my database because I don't think it is properly normalized and because of limitations in my knowledge of relational database theory and mysql. I would appreciate input into the design of the board in general and in particular, ways that the database structure can be improved to facilitate efficient queries and help me develop this application and future application faster Business Logic The bulletin board will be used in the following way Posting bulletins and responses to bulletins Employees or 'users' in offices around the country will be able to post messages to the bulletin board.Bulletins must be posted to a location and categorised- i'll call these "bulletins". Users will be able to post any number of replies to any one bulletin and users will be able to reply to their own bulletin - i'll call these 'replies'. Rating bulletins and replies Users will be able to either 'like' or 'dislike' a bulletin or a reply and the total number of likes or dislikes will be shown for each bulletin or reply. Viewing the bulletin board and responses Bulletins can be displayed chronologically. Users can sort bulletins chronologically or chronologically by the latest reply to that bulletin(let me know if you need more explanation) When a particular bulletin is selected, replies to that bulletin will be displayed chronologically @PerformanceDBA - edited 10:34 est 28/12/10I have begun implementing the data model. I assume that the 6th data model is the physical model because it contains the associative tables. I am going to post any questions that I have below. I will put up a database dump once I am done. I will then put up a list of all the queries that I need to run on the database and begin writing them. I hope you had a good Christmas. I'm in Canada and there's snow! Implementation of Physical model

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• release object of a return method object c

  - by Piero

  in run the app with the analyze build, and Xcode found me a lot of memory leak and there is one in particular that i don't know how solve here it is: - (UIView *) tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section { UIImageView *sectionImage = [[UIImageView alloc] init]; if (section == 0)sectionImage.image = [UIImage imageNamed:@"myImage.png"]; return sectionImage; } so my question is, how i can release this sectionImage? if is the return of the method? EDIT: i have another question, analyze give me another memory leak, i have this: .h @property (nonatomic, retain) NSIndexPath *directCellPath; .m @synthesize directCellPath = _directCellPath; - (id)init{ if ((self = [super initWithNibName:@"MyViewController" bundle:nil])) { self.directCellPath = [[NSIndexPath alloc] init]; } return self; } then in the code i use it and finally in the dealloc i do this: - (void)dealloc { [_directCellPath release]; [super dealloc]; } and give me a memory leak on this line: self.directCellPath = [[NSIndexPath alloc] init]; why if i have deallocated it in the dealloc?

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• Android Signal analysis + some filters.

  - by Profete162

  Hello, as the world cup is the main sport event and the Vuvuzelas are the most annoying sound in the world, I had an idea to remove them definitively by reading this new ( http://www.popsci.com/diy/article/2010-06/simple-software-can-filter-out-vuvuzela-whine) that told us that the sound has some frequencies at 233Hz + 466,932,1864Hz. I have already made a lot of Android application by myself but never touching the signal analysis and filtering part, so here are a few questions, I do not ask for precise answer but maybe links and tutorial to find something to work on. I guess that a new Android phone has the CPU and power to make real-time filtering. 1) How can I intercept the sound coming from the Jack microphone - Line-IN plug- ( I plan to link my TV to my phone with Jack to Jack plug). My question is totally software and coding, I have all the wires and adapters to plug a jack into my android phone Line IN. 2) Are there some Fourier analysis librairies, may I have a look to Java libraries on the web and import them to my Android project? I really apologize because my question seem not precise, but I think that would be something great. Thank you for your answers.

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• Achieving Thread-Safety

  - by Smasher

  Question How can I make sure my application is thread-safe? Are their any common practices, testing methods, things to avoid, things to look for? Background I'm currently developing a server application that performs a number of background tasks in different threads and communicates with clients using Indy (using another bunch of automatically generated threads for the communication). Since the application should be highly availabe, a program crash is a very bad thing and I want to make sure that the application is thread-safe. No matter what, from time to time I discover a piece of code that throws an exception that never occured before and in most cases I realize that it is some kind of synchronization bug, where I forgot to synchronize my objects properly. Hence my question concerning best practices, testing of thread-safety and things like that. mghie: Thanks for the answer! I should perhaps be a little bit more precise. Just to be clear, I know about the principles of multithreading, I use synchronization (monitors) throughout my program and I know how to differentiate threading problems from other implementation problems. But nevertheless, I keep forgetting to add proper synchronization from time to time. Just to give an example, I used the RTL sort function in my code. Looked something like FKeyList.Sort (CompareKeysFunc); Turns out, that I had to synchronize FKeyList while sorting. It just don't came to my mind when initially writing that simple line of code. It's these thins I wanna talk about. What are the places where one easily forgets to add synchronization code? How do YOU make sure that you added sync code in all important places?

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• How to update GUI thread/class from worker thread/class?

  - by user315182

  First question here so hello everyone. The requirement I'm working on is a small test application that communicates with an external device over a serial port. The communication can take a long time, and the device can return all sorts of errors. The device is nicely abstracted in its own class that the GUI thread starts to run in its own thread and has the usual open/close/read data/write data basic functions. The GUI is also pretty simple - choose COM port, open, close, show data read or errors from device, allow modification and write back etc. The question is simply how to update the GUI from the device class? There are several distinct types of data the device deals with so I need a relatively generic bridge between the GUI form/thread class and the working device class/thread. In the GUI to device direction everything works fine with [Begin]Invoke calls for open/close/read/write etc. on various GUI generated events. I've read the thread here (How to update GUI from another thread in C#?) where the assumption is made that the GUI and worker thread are in the same class. Google searches throw up how to create a delegate or how to create the classic background worker but that's not at all what I need, although they may be part of the solution. So, is there a simple but generic structure that can be used? My level of C# is moderate and I've been programming all my working life, given a clue I'll figure it out (and post back)... Thanks in advance for any help.

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• What -W values in gcc correspond to which actual warnings?

  - by SebastianK

  Preamble: I know, disabling warnings is not a good idea. Anyway, I have a technical question about this. Using GCC 3.3.6, I get the following warning: choosing ... over ... because conversion sequence for the argument is better. Now, I want to disable this warning as described in gcc warning options by providing an argument like -Wno-theNameOfTheWarning But I don't know the name of the warning. How can I find out the name of the option that disables this warning? I am not able to fix the warning, because it occurs in a header of an external library that can not be changed. It is in boost serialization (rx(s, count)): template<class Archive, class Container, class InputFunction, class R> inline void load_collection(Archive & ar, Container &s) { s.clear(); // retrieve number of elements collection_size_type count; unsigned int item_version; ar >> BOOST_SERIALIZATION_NVP(count); if(3 < ar.get_library_version()) ar >> BOOST_SERIALIZATION_NVP(item_version); else item_version = 0; R rx; rx(s, count); std::size_t c = count; InputFunction ifunc; while(c-- > 0){ ifunc(ar, s, item_version); } } I have already tried #pragma GCC system_header but this had no effect. Using -isystem instead of -I also does not work. The general question remains is: I know the text of the warning message. But I do not know the correlation to the gcc warning options.

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• Most "thorough" distribution of points around a circle

  - by hippietrail

  This question is intended to both abstract and focus one approach to my problem expressed at "Find the most colourful image in a collection of images". Imagine we have a set of circles, each has a number of points around its circumference. We want to find a metric that gives a higher rating to a circle with points distributed evenly around the circle. Circles with some points scattered through the full 360° are better but circles with far greater numbers of points in one area compared to a smaller number in another area are less good. The number of points is not limited. Two or more points may coincide. Coincidental points are still relevant. A circle with one point at 0° and one point at 180° is better than a circle with 100 points at 0° and 1000 points at 180°. A circle with one point every degree around the circle is very good. A circle with a point every half degree around the circle is better. In my other (colour based question) it was suggested that standard deviation would be useful but with caveat. Is this a good suggestion and does it cope with the closeness of 359° to 1°?

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• Learning libraries without books or tutorials

  - by Kawili-wili

  While many ask questions about where to find good books or tutorials, I'd like to take the opposite tack. I consider myself to be an entry-level programmer ready to move up to mid-level. I have written code in c, c++, c#, perl, python, clojure, vb, and java, so I'm not completely clueless. Where I see a problem in moving to the next level is learning to make better use of the literally hundreds upon hundreds of libraries available out there. I seem paralyzed unless there is a specific example in a book or tutorial to hand-hold me, yet I often read in various forums where another programmer attempts to assist with a question. He/she will look through the docs or scan the available classes/methods in their favorite IDE and seem to grok what's going on in a relatively short period of time, even if they had no previous experience with that specific library or function. I yearn to break the umbilical chord of constantly spending hour upon hour searching and reading, searching and reading, searching and reading. Many times there is no book or tutorial, or if there is, the discussion glosses over my specific needs or the examples shown are too far off the path for the usage I had in mind or the information is outdated and makes use of deprecated components or the library itself has fallen out of mainstream, yet is still perfectly usable (but no docs, books, or tutorials to hand-hold). My question is: In the absence of books or tutorials, what is the best way to grok new or unfamiliar libraries? I yearn to slicken the grok path so I can get down to the business of doing what I love most -- coding.

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• ASP can't connect to SQL Server database

  - by birdus

  I'm trying to get a classic ASP application to connect to a local SQL Server 2008 database. The app and database were built by someone else. I'm just trying to get them installed and running on my machine (Windows 7). I'm getting the following error when when the ASP app tries to connect to the database: Could not connect to database: Error Number: -2147467259 Error Message: [ConnectionOpen (Connect()).] does not exist or access denied. I don't see any messages in the Windows Event Viewer. I'm looking at: Event Viewer-Windows Logs-Application. It's a fresh database install using a simple restore. The SQL Server install uses the default instance. SQL Server and Windows authentication are both allowed. I left the existing connection string (in the ASP code) in tact and just tried adding that to my SQL Server installation. Here's the connection string: strConn = "PROVIDER=SQLOLEDB;SERVER=localhost;UID=TheUser;PWD=ThePassword;DATABASE=TheDatabase;" To add that user to SQL Server, I went to Security/Logins in SSMS and added the user and the password. I selected the database in question as the Default database. I thought that might do the trick, but it didn't. Then, I went into TheDatabase, then went into Security there. I added a new user there, referencing the new user I had already added in server Security. Under Owned Schemas, I clicked db_owner and under Role Members I checked db_accessadmin and db_owner. None of this gave the ASP application access to the database. The sid values match in sys.database_principals and sys.server_principals for the login in question. I am able to login to SSMS using this login. The app needs to execute selects against the database like this: oConn.Execute('select * from someTable') I'm not a DBA and am sort of grasping at straws here. How do I get this thing connected? Thanks, Jay

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• Why can't I display a unicode character in the Python Interpreter on Mac OS X Terminal.app?

  - by apphacker

  If I try to paste a unicode character such as the middle dot: · in my python interpreter it does nothing. I'm using Terminal.app on Mac OS X and when I'm simply in in bash I have no trouble: :~$ · But in the interpreter: :~$ python Python 2.6.1 (r261:67515, Feb 11 2010, 00:51:29) [GCC 4.2.1 (Apple Inc. build 5646)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> ^^ I get nothing, it just ignores that I just pasted the character. If I use the escape \xNN\xNN representation of the middle dot '\xc2\xb7', and try to convert to unicode, trying to show the dot causes the interpreter to throw an error: >>> unicode('\xc2\xb7') Traceback (most recent call last): File "<stdin>", line 1, in <module> UnicodeDecodeError: 'ascii' codec can't decode byte 0xc2 in position 0: ordinal not in range(128) I have setup 'utf-8' as my default encoding in sitecustomize.py so: >>> sys.getdefaultencoding() 'utf-8' What gives? It's not the Terminal. It's not Python, what am I doing wrong?! This question is not related to this question, as that indivdiual is able to paste unicode into his Terminal.

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• Something about Stream

  - by sforester

  I've been working on something that make use of streams and I found myself not clear about some stream concepts( you can also view another question posted by me at http://stackoverflow.com/questions/2933923/about-redirected-stdout-in-system-diagnostics-process ). 1.how do you indicate that you have finished writing a stream, writing something like a EOF? 2.follow the previous question, if I have written a EOF(or something like that) to a stream but didn't close the stream, then I want to write something else to the same stream, can I just start writing to it and no more set up required? 3.if a procedure tries to read a stream(like the stdin ) that no one has written anything to it, the reading procedure will be blocked,finally some data arrives and the procedure will just read till the writing is done,which is indicated by getting a return of 0 count of bytes read rather than being blocked, and now if the procedure issues another read to the same stream, it will still get a 0 count and return immediately while I was expecting it will be blocked since no one is writing to the stream now. So does the stream holds different states when the stream is opened but no one has written to it yet and when someone has finished a writing session? I'm using Windows the .net framework if there will by any thing platform specific. Thanks a lot!

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• Add xml-stylesheet and get standalone = yes.

  - by tumba25

  The code at the bottom is what I have. I removed the creation of all tags. At the top in the xml file I get.<?xml version="1.0" encoding="UTF-8" standalone="no"?> Note that standalone is no, even thou I have it set to yes. The first question: How do I get standalone = yes? I would like to add <?xml-stylesheet type="text/xsl" href="my.stylesheet.xsl"?> at line two in the xml file. Second question: How do I do that? Some useful links? Anything? DocumentBuilderFactory dbfac = DocumentBuilderFactory.newInstance(); DocumentBuilder docBuilder = dbfac.newDocumentBuilder(); Document doc = docBuilder.newDocument(); <cut> TransformerFactory transfac = TransformerFactory.newInstance(); transfac.setAttribute("indent-number", new Integer(2)); Transformer trans = transfac.newTransformer(); trans.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no"); trans.setOutputProperty(OutputKeys.STANDALONE, "yes"); trans.setOutputProperty(OutputKeys.INDENT, "yes"); trans.setOutputProperty(OutputKeys.CDATA_SECTION_ELEMENTS, "name"); FileOutputStream fout = new FileOutputStream(filepath); BufferedOutputStream bout= new BufferedOutputStream(fout); trans.transform(new DOMSource(doc), new StreamResult(new OutputStreamWriter(bout, "utf-8")));

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• Java - How to declare table[i][j] elements as instance variables?

  - by JDelage

  All, I am trying to code a Connect4 game. For this, I have created a P4Game class and a P4Board class which represents the i X j dimensions of the Connect4 board. In P4Game, I have the following: public class P4Game{ //INSTANCE VARIABLES private int nbLines; private int nbColumns; private P4Board [][] position; //CONSTRUCTOR public P4Game(int nbLines, int nbColumns){ this.nbColumns = nbColumns; this.nbLines = nbLines; P4Board [][] position = new P4Board [nbLines][nbColumns]; //Creates the table to receive the instances of the P4Board object.*/ for (int i=0; i<nbLines; i++){ for (int j=0; j<nbColumns; j++){ this.position[i][j] = new P4Board(i,j); //Meant to create each object at (line=i, column=j) } } } This causes a NullPointerException in the nested loops where I mention this.position[i][j]. I reference those objects in other methods of this class so I need them to be instance variables. I suppose the exception is due to the fact that I have not listed the table element position[i][j] as an instance variable at the beginning of the class. my question to people here is (1) is my assumption correct, and if so (2) what would be the syntax to declare instance variables of this form? Thank you all for your help with what I realize is a very basic question. Hopefully it will also benefit other newbies. Cheers, JDelage

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• Is it possible to send OSC commands to an iPad via the Camera Connection Kit?

  - by HELVETICADE

  I'm building a small controller device that I'd like to partner with a computer. I've settled on using OSC out from my custom built hardware and am pretty satisfied with what I can get from WOscLib. Two goals I'd like to achieve are portability and a very nice ratio between battery:computing power, and this has lured me towards using iPhoneOS to accomplish my goals. I think the iPad would suit my needs perfectly, except that using wifi to broadcast OSC out from my device requires that device to be connected to a third device with a wifi chip, and this would destroy the goal of portability, whilst also introducing potential latency and stability headaches. My question is pretty simple: Can I push OSC commands FROM my controller TO an iPad via USB and the Camera Connection Kit? If I could accomplish this, the two major goals of my project would be fulfilled very nicely. This seems like it should be a simple little question, but researching this obsessively over the past few weeks has left me more almost more uncertain than if I had done no research at all. I'd really like some more confidence before I go down this route, and it seems like it should be possible. Any insight would be very, very appreciated.

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• "variable tracking" is eating my compile time!

  - by wowus

  I have an auto-generated file which looks something like this... static void do_SomeFunc1(void* parameter) { // Do stuff. } // Continues on for another 4000 functions... void dispatch(int id, void* parameter) { switch(id) { case ::SomeClass1::id: return do_SomeFunc1(parameter); case ::SomeClass2::id: return do_SomeFunc2(parameter); // This continues for the next 4000 cases... } } When I build it like this, the build time is enormous. If I inline all the functions automagically into their respective cases using my script, the build time is cut in half. GCC 4.5.0 says ~50% of the build time is being taken up by "variable tracking" when I use -ftime-report. What does this mean and how can I speed compilation while still maintaining the superior cache locality of pulling out the functions from the switch? EDIT: Interestingly enough, the build time has exploded only on debug builds, as per the following profiling information of the whole project (which isn't just the file in question, but still a good metric; the file in question takes the most time to build): Debug: 8 minutes 50 seconds Release: 4 minutes, 25 seconds

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• select all values from a dimension for which there are facts in all other dimensions

  - by ideasculptor

  I've tried to simplify for the purposes of asking this question. Hopefully, this will be comprehensible. Basically, I have a fact table with a time dimension, another dimension, and a hierarchical dimension. For the purposes of the question, let's assume the hierarchical dimension is zip code and state. The other dimension is just descriptive. Let's call it 'customer' Let's assume there are 50 customers. I need to find the set of states for which there is at least one zip code in which EVERY customer has at least one fact row for each day in the time dimension. If a zip code has only 49 customers, I don't care about it. If even one of the 50 customers doesn't have a value for even 1 day in a zip code, I don't care about it. Finally, I also need to know which zip codes qualified the state for selection. Note, there is no requirement that every zip code have a full data set - only that at least one zip code does. I don't mind making multiple queries and doing some processing on the client side. This is a dataset that only needs to be generated once per day and can be cached. I don't even see a particularly clean way to do it with multiple queries short of simply brute-force iteration, and there are a heck of a lot of 'zip codes' in the data set (not actually zip codes, but the there are approximately 100,000 entries in the lower level of the hierarchy and several hundred in the top level, so zipcode-state is a reasonable analogy)

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• Centralized Exception handling for Eclipse plug-in

  - by Svilen

  Hello, At first I thought this would be question often asked, however trying (and failing) to look up info on this proved me wrong. Is there a mechanism in Eclipse platform for centralized exception handling of exceptions? For example... You have plug-in project which connects to a DB and issues queries, results of which are used to populate some e.g. views. This is like the most common example ever. :) Queries are executed almost for any user action, from every UI control the plug-in provides. Most likely the DB Query API will have some specific to the DB SomeDBGeneralException declared as being thrown by it. That's OK, you can handle those according to whatever your software design is. But how about unchecked exceptions which are likely to occur, e.g. , when communication with DB suddenly breaks for some network related reason? What if in such case one would like to catch those exceptions in a central place and for example provide user friendly message to the user (rather than the low level communication protocol api messages) and even some possible actions the user could execute in order to deal with the specific problem? Thinking in Eclipse platform context, the question may be rephrased as "Is there an extension point like "org.eclipse.ExceptionHandler" which allows to declare exception handlers for specific (some kind of filtering support) exceptions giving a lot of flexibility with the actual handling?"

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• MySQL SELECT combining 3 SELECTs INTO 1

  - by Martin Tóth

  Consider following tables in MySQL database: entries: creator_id INT entry TEXT is_expired BOOL other: creator_id INT entry TEXT userdata: creator_id INT name VARCHAR etc... In entries and other, there can be multiple entries by 1 creator. userdata table is read only for me (placed in other database). I'd like to achieve a following SELECT result: +------------+---------+---------+-------+ | creator_id | entries | expired | other | +------------+---------+---------+-------+ | 10951 | 59 | 55 | 39 | | 70887 | 41 | 34 | 108 | | 88309 | 38 | 20 | 102 | | 94732 | 0 | 0 | 86 | ... where entries is equal to SELECT COUNT(entry) FROM entries GROUP BY creator_id, expired is equal to SELECT COUNT(entry) FROM entries WHERE is_expired = 0 GROUP BY creator_id and other is equal to SELECT COUNT(entry) FROM other GROUP BY creator_id. I need this structure because after doing this SELECT, I need to look for user data in the "userdata" table, which I planned to do with INNER JOIN and select desired columns. I solved this problem with selecting "NULL" into column which does not apply for given SELECT: SELECT creator_id, COUNT(any_entry) as entries, COUNT(expired_entry) as expired, COUNT(other_entry) as other FROM ( SELECT creator_id, entry AS any_entry, NULL AS expired_entry, NULL AS other_enry FROM entries UNION SELECT creator_id, NULL AS any_entry, entry AS expired_entry, NULL AS other_enry FROM entries WHERE is_expired = 1 UNION SELECT creator_id, NULL AS any_entry, NULL AS expired_entry, entry AS other_enry FROM other ) AS tTemp GROUP BY creator_id ORDER BY entries DESC, expired DESC, other DESC ; I've left out the INNER JOIN and selecting other columns from userdata table on purpose (my question being about combining 3 SELECTs into 1). Is my idea valid? = Am I trying to use the right "construction" for this? Are these kind of SELECTs possible without creating an "empty" column? (some kind of JOIN) Should I do it "outside the DB": make 3 SELECTs, make some order in it (let's say python lists/dicts) and then do the additional SELECTs for userdata? Solution for a similar question does not return rows where entries and expired are 0. Thank you for your time.

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• Auto increment with a Unit Of Work

  - by Derick

  Context I'm building a persistence layer to abstract different types of databases that I'll be needing. On the relational part I have mySQL, Oracle and PostgreSQL. Let's take the following simplified MySQL tables: CREATE TABLE Contact ( ID varchar(15), NAME varchar(30) ); CREATE TABLE Address ( ID varchar(15), CONTACT_ID varchar(15), NAME varchar(50) ); I use code to generate system specific alpha numeric unique ID's fitting 15 chars in this case. Thus, if I insert a Contact record with it's Addresses I have my generated Contact.ID and Address.CONTACT_IDs before committing. I've created a Unit of Work (amongst others) as per Martin Fowler's patterns to add transaction support. I'm using a key based Identity Map in the UoW to track the changed records in memory. It works like a charm for the scenario above, all pretty standard stuff so far. The question scenario comes in when I have a database that is not under my control and the ID fields are auto-increment (or in Oracle sequences). In this case I do not have the db generated Contact.ID beforehand, so when I create my Address I do not have a value for Address.CONTACT_ID. The transaction has not been started on the DB session since all is kept in the Identity Map in memory. Question: What is a good approach to address this? (Avoiding unnecessary db round trips) Some ideas: Retrieve the last ID: I can do a call to the database to retrieve the last Id like: SELECT Auto_increment FROM information_schema.tables WHERE table_name='Contact'; But this is MySQL specific and probably something similar can be done for the other databases. If do this then would need to do the 1st insert, get the ID and then update the children (Address.CONTACT_IDs) – all in the current transaction context.

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• Boost Asio UDP retrieve last packet in socket buffer

  - by Alberto Toglia

  I have been messing around Boost Asio for some days now but I got stuck with this weird behavior. Please let me explain. Computer A is sending continuos udp packets every 500 ms to computer B, computer B desires to read A's packets with it own velocity but only wants A's last packet, obviously the most updated one. It has come to my attention that when I do a: mSocket.receive_from(boost::asio::buffer(mBuffer), mEndPoint); I can get OLD packets that were not processed (almost everytime). Does this make any sense? A friend of mine told me that sockets maintain a buffer of packets and therefore If I read with a lower frequency than the sender this could happen. ¡? So, the first question is how is it possible to receive the last packet and discard the ones I missed? Later I tried using the async example of the Boost documentation but found it did not do what I wanted. http://www.boost.org/doc/libs/1_36_0/doc/html/boost_asio/tutorial/tutdaytime6.html From what I could tell the async_receive_from should call the method "handle_receive" when a packet arrives, and that works for the first packet after the service was "run". If I wanted to keep listening the port I should call the async_receive_from again in the handle code. right? BUT what I found is that I start an infinite loop, it doesn't wait till the next packet, it just enters "handle_receive" again and again. I'm not doing a server application, a lot of things are going on (its a game), so my second question is, do I have to use threads to use the async receive method properly, is there some example with threads and async receive? Thanks for you attention.

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• How does one implement storage/retrieval of smart-search/mailbox features?

  - by humble_coder

  Hi All, I have a question regarding implementation of smart-search features. For example, consider something like "smart mailboxes" in various email applications. Let's assume you have your data (emails) stored in a database and, depending on the field for which the query will be created, you present different options to the end user. At the moment let's assume the Subject, Verb, Object approach… For instance, say you have the following: SUBJECTs: message, to_address, from_address, subject, date_received VERBs: contains, does_not_contain, is_equal_to, greater_than, less_than OBJECTs: ??????? Now, in case it isn't clear, I want a table structure (although I'm not opposed to an external XMLesque file of some sort) to store (and later retrieve/present) my criteria for smart searches/mailboxes for later use. As an example, using SVO I could easily store then reconstruct a query for "date between two dates" -- simply use "date greater than" AND "date less than". However, what if, in the same smart search, I wanted a "between" OR'ed with another criterion? You can see that it might get out of hand -- not necessarily in the query creation (as that is rather simplistic), but in the option presentation and storage mechanism. Perhaps I need to think more on a more granular level. Perhaps I need to simply allow the user to select AND or OR for each entry independently instead of making it an ALL OR NOTHING type smart search (i.e. instead of MATCH ALL or MATCH ANY, I need to simply allow them to select -- I just don't want it to turn into a Hydra). Any input would be most appreciated. My apologies if the question is a bit incoherent. It is late, and I my brain is toast. Best.

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• How do I find the .max of an attribute value among a group of different Models?

  - by Angela

  Hi, everyone: I am also open to just straight-up refactoring what I'm finding to be pretty repetitive, but to give a baseline of how it's working.... I have for every contact a Campaign, which has_many of three types of Models: Email, Call, and Letter. When an Email (Call or Letter) has been executed for a specific contact, I have a Contact_Email(_or_Call_or_Letter) which belongs to both the Contact and the Model (Email_or_Call_or_Letter). Each Contact_Email for example pairing has a :date_sent attribute. So does each Contact_Call and Contact_Letter. How do I find the latest of all of them? Here is the code I wrote that can find the latest Email and my finding retyping similar code for Call and Letter, but then stuck on how to do a .max on all of them: def last_email(contact) #get campaign the contact belongs to @campaign = Campaign.find_by_id(contact.campaign_id) @last_email = ContactEmail.find(:last, :conditions => "contact_id = #{contact.id}", :order => "date_sent DESC") @last_call = ContactCall.find(:last, :conditions => "contact_id = #{contact.id}", :order => "date_sent DESC") @last_letter = ContactLetter.find(:last, :conditions => "contact_id = #{contact.id}", :order => "date_sent DESC") # how do I get the latest of all of these to display? if @last_sent_email.nil? return "no email sent" else return @last_sent_email.date_sent end end Question 1: With what I have, how can I find effectively @last_event given I can find the last Email, last Call, and last Letter for every contact? Question 2: How can I remove the repetitive code that I have to write for each Model?

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• C# class can not disguise to be another class because GetType method cannot be override

  - by zinking

  there is a statement in the CLR via C# saying in C#, one class cannot disguise to be another, because GetType is virutal and thus it cannot be override but I think in C# we can still hide the parent implementation of GetType. I must missed something if I hide the base GetType implementation then I can disguise my class to be another class, is that correct? The key here is not whether GetType is virutal or not, the question is can we disguise one class to be another in C# Following is the NO.4 answer from the possible duplicate, so My question is more on this. is this kind of disguise possible, if so, how can we say that we can prevent class type disguise in C# ? regardless of the GetType is virtual or not While its true that you cannot override the object.GetType() method, you can use "new" to overload it completely, thereby spoofing another known type. This is interesting, however, I haven't figured out how to create an instance of the "Type" object from scratch, so the example below pretends to be another type. public class NotAString { private string m_RealString = string.Empty; public new Type GetType() { return m_RealString.GetType(); } } After creating an instance of this, (new NotAString()).GetType(), will indeed return the type for a string. share|edit|flag answered Mar 15 at 18:39 Dr Snooze 213 By almost anything that looks at GetType has an instance of object, or at the very least some base type that they control or can reason about. If you already have an instance of the most derived type then there is no need to call GetType on it. The point is as long as someone uses GetType on an object they can be sure it's the system's implementation, not any other custom definition. – Servy Mar 15 at 18:54 add comment

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